Signaling devices that involve alert mechanisms which emit audible and/or visual signals are used in a broad range of mechanical, hydraulic and electrically controlled devices and systems. A typical signaling device includes an alert mechanism that consists of a selectively activated speaker or other sound-generating device, such as a piezo-electric buzzer, coupled with an electrical power system. Common examples of audible alert mechanisms include any of the various beepers, buzzers, bells, or loudspeakers activated in a work machine when a particular operating condition is detected. For instance, in many work machines a bell is activated within earshot of an operator to alert him or her to a particular engine condition.
Virtually any aspect of a work machine can be monitored and have an associated audible or visual alert responsive to conditions such as engine temperature, oil pressure, fuel pressure and level, a hydraulic system condition, and even tire pressure. Increasingly, the various condition sensors known in the art have their outputs interpreted by an algorithm in an electronic control module (ECM). The ECM thus determines whether predetermined conditions have been met and directs a signaling device to activate an alert mechanism if necessary. Specifically, it would be useful to monitor a work machine's electro-hydraulic steering system and notify an operator when a primary system has encountered a malfunction and the machine is operating via a secondary redundant system. In this way an operator can get a machine serviced immediately.
A drawback of many known signaling devices is that the electrical circuit depends upon the machine's electrical power supply for the power necessary to activate the alert mechanism. This can be problematic if there is a mechanical fault or an undetected break in the electrical system. For instance, debris encountered by a work machine may unknowingly cut a wire that is part of the electrical circuit. In such a case, the operator might not be aware of a condition that could require his attention because the signaling device simply does not have the power required to activate an alert mechanism. Alarm failure may result in the need for costly repairs and significant time delays if, for example, a system fails before the operator realizes a problem exists because he is relying on an alarm requiring power from a faulty circuit.
U.S. Pat. No. 3,702,469 to Golja is directed to an alarm circuit operable to sound a bell when redundant power supplies fail. Golja utilizes switching transistors to detect increases and decreases in supply voltages that are greater than prescribed amounts, which are in turn indicative of a failure. While Golja sets forth a design having certain applications, particularly in systems requiring dual electrical power supplies, there is always room for improvement. For example, Golja would not be readily incorporated into existing work machines having a single primary electrical power source.
The present disclosure is directed to one or more of the problems set forth above.